1. Field of the Invention
The present invention relates to a power semiconductor device for performing power conversion and, more particularly, to protection to serge in the power semiconductor device.
2. Related Art
A general power semiconductor device which performs power conversion includes an inverter circuit having a parallel connected plurality of half bridge circuits each including serially connected two power semiconductor elements, and a control circuit which drives the power semiconductor elements in the inverter circuit.
A protection function to an overcurrent is generally arranged for a power semiconductor device. In order to detect amount of a current flowing through the power semiconductor element for overcurrent protection, for example, a method of using a voltage generated in a shunt resistor connected to an inverter circuit is known. FIG. 3 shows a configuration of a conventional power semiconductor device for detecting an overcurrent by using such a method.
As shown in FIG. 3, the power semiconductor device has power semiconductor elements SW1 and SW2 which are on a low voltage side and a high voltage side, respectively, control circuits IC1 and IC2 for driving and controlling the respective power semiconductor elements SW1 and SW2, and free-wheeling diodes FW1 and FW2 of the power semiconductor elements SW1 and SW2. The power semiconductor device outputs an output voltage obtained by controlling the switching operations of the power semiconductor elements SW1 and SW2, from an output terminal VS.
In the power semiconductor device, a shunt resistor R1 is connected between an emitter terminal N1 of the power semiconductor element SW1 on the low voltage side and a reference potential terminal N connected to the low potential side of a DC power supply (to be referred to as a xe2x80x9ccontrol power supplyxe2x80x9d hereinafter) for driving the control circuits IC1 and IC2. A voltage VR1 proportional to amount of a current flowing in the power semiconductor element SW1 is generated across the shunt resistor R1. As shown in FIG. 3, a parasitic inductance L exists between the emitter terminal N1 of the power semiconductor element SW1 and the shunt resistor R1.
The control circuit IC1 has a terminal VIN to which a control power supply voltage is input, a current detection terminal CIN, and an output terminal OUT1 for outputting a control signal for controlling the power semiconductor element SW1. The control circuit IC1 has an overcurrent protection function, detects a current flowing in the semiconductor element SW1 with a voltage applied to the current detection terminal CIN, and outputs a control signal for turning off the semiconductor element SW1 when an overcurrent flowing in the semiconductor element SW1 is detected. More specifically, the voltage VR1 generated across the shunt resistor R1 is applied to the current detection terminal CIN of the control circuit IC1 through a filter circuit including a resistor R2 and a capacitor C1. When the voltage of the current detection terminal CIN exceeds a reference level, the overcurrent protection function of the control circuit IC1 serves becomes active to cut off the output OUT1 thereof.
When the overcurrent protection function described above operates, a surge voltage with a relatively high level may occur between the terminals N1 and N due to the parasitic inductance L of a conductor or wire extending from the emitter terminal N1 to the resistor R1. A control power supply voltage VD is applied between the reference potential terminal N of the control power supply voltage and a power supply terminal VCC through a smoothing capacitor C2. Therefore, a high voltage obtained by superposing the control power supply voltage VD to the surge voltage applied between the terminals N1 and N is applied between the terminals N1 and VCC. Hence, a very high surge voltage may be applied between the terminals N1 and N, and thus can break the control circuit IC1.
The present invention has been made to solve the above problems, and has an object to provide a power semiconductor device capable of preventing a control circuit which controls a switching operation of semiconductor elements from being broken by a surge voltage applied between predetermined terminals of the control circuit.
In the first aspect of the invention, provided is a power semiconductor device comprising a half bridge circuit, a control circuit, and a noise removal circuit. The half bridge circuit includes a switching element on a low voltage side and a switching element on a high voltage side. Those switching elements are serially connected. The control circuit is operable to control a switching operation of the switching element on a low voltage side in the half bridge circuit. The control circuit has a supply-voltage receiving terminal connected to a high voltage side of a power supply for driving the control circuit. The noise removal circuit is operable to remove noise generated on a conductor connected to a low voltage side terminal of the switching element on a low voltage side. The noise removal circuit is interposed between the supply-voltage receiving terminal of the control circuit and the low voltage side terminal of the switching element on a low voltage side. In the power semiconductor device, the noise removal circuit may includes a zener diode or a capacitor.
According to the semiconductor device in the first aspect, even though a surge voltage is generated between the power supply receiving terminal of the control circuit and the low voltage terminal of the switching element on the low voltage side, the noise reduction means can suppress a sharp variation in voltage to protect the control circuit from a break.
In the second aspect of the invention, provided is a power semiconductor device including a half bridge circuit, a control circuit, and a noise removal circuit. The half bridge circuit includes a switching element on a low voltage side and a switching element on a high voltage side. Those switching elements are serially connected. The control circuit is operable to control a switching operation of the switching element on a low voltage side in the half bridge circuit. The control circuit has a reference potential terminal connected to a reference potential terminal of a power supply for driving the control circuit. The reference potential terminal provides a reference potential. The noise removal circuit is operable to remove noise generated on a conductor connected to a low voltage side terminal of the switching element on a low voltage side. The noise removal circuit is interposed between the reference potential terminal of the control circuit and the low voltage side terminal of the switching element on a low voltage side. In a power semiconductor device, the noise removal circuit may include a capacitor.
According to the semiconductor device in the second aspect, a sharp variation in voltage generated between the reference potential terminal of the control circuit for controlling the switching element on the low voltage side and the low voltage terminal of the switching element on the low voltage side can be suppressed. Accordingly, a control circuit can be prevented from being broken by surge.